1. Field of the Invention
The present invention relates to a semiconductor device having a circuit which is configured of thin film transistors (hereinbelow, often abbreviated to xe2x80x9cTFTsxe2x80x9d). By way of example, it relates to the constructions of an electrooptic device which is typified by a liquid crystal display panel, and an electronic equipment in which such an electrooptic device is installed as a component.
Incidentally, here in this specification, the expression xe2x80x9csemiconductor devicexe2x80x9d is intended to signify general devices which can function by utilizing semiconductor properties, and it shall cover all of electrooptic devices, semiconductor circuits and electronic equipment within its category.
2. Description of the Related Art
In recent years, notice has been taken of technology wherein thin film transistors (TFTs) are constructed using a semiconductor thin film (several to a few hundred [nm] thick) which is formed on a substrate having an insulating surface. The TFTs are extensively applied to ICs (integrated circuits) and electronic devices such as electrooptic devices, and it is especially hurried to develop them as the switching elements of an image display device.
In, for example, a liquid crystal display device, attempts have been made to apply TFTs to all sorts of electric circuits such as a pixel unit in which pixels arrayed in the shape of a matrix are individually controlled, a driver circuit which controls the pixel unit, and a logic circuit (including a processor circuit, a memory circuit, etc.) which processes data signals fed from outside.
Besides, there has been known a construction (system-on-panel) in which the above circuits (pixel unit, driver circuit, etc.) are packaged on a single substrate. In the pixel unit, the pixel plays the role of retaining information sent from the driver circuit. Herein, unless the OFF current of the TFT connected to the pixel is sufficiently small, the information cannot be retained, and a good display cannot be presented.
On the other hand, in the driver circuit, a high mobility is required of the TFTs. As the mobility is higher, the structure of this circuit can be simplified more, and the display device can be operated at a higher speed.
As stated above, the TFTs arranged in the driver circuit and those arranged in the pixel unit are different in the required properties. More specifically, the TFTs arranged in the pixel unit need not have a very high mobility, but their requisites are that the OFF current is small and that the value thereof is uniform throughout the pixel unit. In contrast, the TFTs of the driver circuit located around the pixel unit take preference of the mobility over the OFF current, and their requisite is that the mobility is high.
It has been difficult, however, to manufacture the TFTs of the preferential mobility and the TFTs of the small OFF current on an identical substrate at a high productivity and without spoiling their reliabilities, by employing a fabricating method in the prior art.
As understood from the foregoing, a quite new construction having hitherto been nonexistent is required in order to incarnate a system-on-panel which has a built-in logic circuit.
In compliance with such a requirement, the present invention has for its object to provide an electrooptic device represented by AM-LCD (Active-Matrix Liquid Crystal Display), the respective circuits of which are formed using TFTs of appropriate structures in accordance with their functions, and which is accordingly endowed with a high reliability.
The construction of the present invention disclosed in this specification consists in a semiconductor device having a driver circuit and a pixel unit which are formed on an identical substrate, characterized in:
that a channel forming region of at least one TFT (thin film transistor) included in said driver circuit is made of a crystalline semiconductor film; and
that a channel forming region of a TFT included in said pixel unit is made of an amorphous semiconductor film.
Besides, in the above construction, the semiconductor device is characterized in that said channel forming region of said at least one TFT included in said driver circuit is formed via a processing step of irradiation with a laser beam or an intense light beam similar thereto.
Also, in the above construction, the semiconductor device is characterized in that the channel forming regions of said at least one TFT included in said driver circuit and said TFT included in said pixel unit are made of a semiconductor film which is formed by sputtering.
Further, in the above construction, the semiconductor device is characterized in that gate insulating films of said at least one TFT included in said driver circuit and said TFT included in said pixel unit are made of an insulating film which is formed by sputtering.
Still further, in the above construction, the semiconductor device is characterized in that said crystalline semiconductor film is of polysilicon, while said amorphous semiconductor film is of amorphous silicon.
Yet further, in the above construction, the semiconductor device is characterized by being a display device of active matrix type, for example, an EL (electroluminescent) display device or a liquid crystal display device.
In addition, the construction of the present invention for realizing the above structure consists in:
a method of fabricating a semiconductor device having a driver circuit and a pixel unit which are formed on an identical substrate, characterized by comprising:
the first step of forming an amorphous semiconductor film on an insulating surface of said substrate;
the second step of irradiating a selected part of said amorphous semiconductor film with either of a laser beam and an intense light beam similar thereto, thereby to turn the part of said amorphous semiconductor film into a crystalline semiconductor film;
the third step of patterning said crystalline semiconductor film, thereby to form a semiconductor layer of said driver circuit, and also patterning the resulting amorphous semiconductor film, thereby to form a semiconductor layer of said pixel unit;
the fourth step of forming an insulating film on the semiconductor layers; and
the fifth step of forming gate electrodes on said insulating film.
Besides, in the above construction, the fabricating method is characterized in that said fourth step is implemented by sputtering.
Another construction of the present invention consists in:
a method of fabricating a semiconductor device having a driver circuit and a pixel unit which are formed on an identical substrate, characterized by comprising:
the first step of forming an amorphous semiconductor film on an insulating surface of said substrate;
the second step of forming an insulating film on said amorphous semiconductor film;
the third step of irradiating a selected part of said amorphous semiconductor film with either of a laser beam and an intense light beam similar thereto through said insulating film, thereby to turn the part of said amorphous semiconductor film into a crystalline semiconductor film;
the fourth step of patterning said crystalline semiconductor film, thereby to form a semiconductor layer of said driver circuit, and also patterning the resulting amorphous semiconductor film, thereby to form a semiconductor layer of said pixel unit; and
the fifth step of forming gate electrodes on said insulating film.
Besides, in the above construction concerning the fabrication the fabricating method is characterized in that said second step is implemented by sputtering.
Also, in each of the above constructions concerning the fabrication, the fabricating method is characterized in that said first step is implemented by sputtering.
Still another construction of the present invention consists in:
a method of fabricating a semiconductor device having a driver circuit and a pixel unit which are formed on an identical substrate, characterized by comprising:
the first step of forming gate electrodes on an insulating surface of said substrate;
the second step of forming an insulating film on said gate electrodes;
the third step of forming an amorphous semiconductor film on said insulating film;
the fourth step of irradiating a selected part of said amorphous semiconductor film with either of a laser beam and an intense light beam similar thereto, thereby to turn the part of said amorphous semiconductor film into a crystalline semiconductor film; and
the fifth step of patterning said crystalline semiconductor film, thereby to form a semiconductor layer of said driver circuit, and also patterning the resulting amorphous semiconductor film, thereby to form a semiconductor layer of said pixel unit.
Besides, in each of the constructions concerning the fabrication, the fabricating method is characterized by comprising after said fifth step:
the sixth step of doping selected regions to become source and drain regions, with elements which belong to the 15th Group and 13th Group of elements; and
the seventh step of activating said elements which belong to said 15th Group and 13th Group, and with which the semiconductor layers have been doped.
Also, in each of the constructions concerning the fabrication, the fabricating method is characterized in that said semiconductor device is a liquid crystal display device.
Further, in each of the constructions concerning the fabrication, the fabricating method is characterized by comprising after said seventh step of activating said elements:
the eighth step of forming an interlayer insulating film over the active layers;
the ninth step of forming a pixel electrode on said interlayer insulating film;
the tenth step of forming an EL layer on said pixel electrode; and
the eleventh step of forming either of a cathode and an anode on said EL layer.
Still further, in each of the above constructions concerning the fabrication, the fabricating method is characterized in that said semiconductor device is an EL display device.